Atoms and Elements Properties and Changes

Scientific Terminology Control – an event that is used as a constant and unchanging standard of comparison in scientific experimentation. Variable - capable of being varied or changed; alterable Hypothesis - A tentative explanation that accounts for a set of facts and can be tested by further investigation. Trial - the act of trying, testing, or putting to the proof.

Nature of Matter Particle Theory of Matter 1.All matter is made up of tiny particles 2.Each pure substance has its own kind of particles 3.Particles attract each other 4.Particles are always moving 5.Particles at a higher temperature move faster on average than particles at a lower temperature

Nature of Matter Scientific Model – particle theory is one example of a SM It helps us to picture a process in nature we can not see directly. Matter – solid, liquid, gas or plasma

Nature of Matter Physical change –No new substance is being formed

Chemical change –At least one new substance, with new properties, is formed. –If two of the following are true, then a chemical change has probably occurred: –Heat is absorbed or produced –Starting material is used up –New colour appears –Material with new properties forms –Gas bubbles form in a liquid –Grains of solid appear in liquid

Nature of Matter Physical Properties – observed and measured without forming a new substance –Colour = for gases the colour is often clear –Density = amount of matter that occupies a certain space Qualitative physical property –Described but not measured

Mixtures Mixtures make up most of the matter in the world Solutions –Solvent – substance that does the dissolving –Solute – substance that dissolves –Water + Salt = Chemical change? Properties have changed however they can still be separated

Chemical Formulas Chemical Formula = uses symbols and numbers to represent the composition of a pure substance –Definite proportions Molecule = smallest independent unit of a pure substance –Electrolysis separates water molecules as the added energy rips the molecules apart

Different kinds of elements Metals = conduct electricity and heat, hammered into sheets (malleability), stretched into wires (ductility), shiny lustre, and are solids at room temperature. Non-metals = Some are gases at room temp, not shiny, not stretched into wires, poor electricity and heat conductors Metalloids = in-between a metal and a non-metal

Families of Metals Characteristics –Group 1  alkali metals React rapidly with water to produce hydrogen Sodium is stored in kerosene so no water vapour contact –Group 17  halogens Most reactive non-metals –Chlorine & Bromine can cause many serious problems Na (very reactive) + Cl (very reactive) = NaCl (table salt) –Group 18  noble gases Chemically calm Calm = noble in historic times